Prostaglandins (PGs) are shown to influence sperm motility, contractility of the smooth muscle layers surrounding the seminiferous tubules and growth of both the seminal vesicle and the ventral prostate. PGs are produced by two distinct isoforms of cyclooxygenase (COX), including constitutively expressed COX-1 and inducible COX-2. To investigate the potential role of COX-2 in male reproductive tract maturation, we evaluated its expression in rats at pre-pubertal (14 days old), peri-pubertal (21, 28 and 35 days old) and post-pubertal (62 days old) stages. COX-2 was constitutively expressed in the initial segment of the epididymis, caput epididymidis and vas deferens at all stages of maturation. Its expression was mild in 14-day-old rats but its intensity markedly increased at 28 days and remained elevated afterwards. There was no COX-2 staining in the testis, rete testis, efferent ducts or cauda epididymidis. These data suggest that COX-2 derived PGs may be involved in the pubertal development of the epididymis, but not in the more apical regions of the excurrent duct system, including the rete testis and efferent ductules.